On Tue, May 07, 2024 at 10:37:54AM +0200, Alexander Stein wrote: > Hi Michael, > > Am Montag, 6. Mai 2024, 15:34:30 CEST schrieb Michael Walle: > > Some bridges have very strict power-up reqirements. In this case, the > > Toshiba TC358775. The reset has to be deasserted while *both* the DSI > > clock and DSI data lanes are in LP-11 mode. After the reset is relased, > > the bridge needs the DSI clock to actually be able to process I2C > > access. This access will configure the DSI side of the bridge during > > which the DSI data lanes have to be in LP-11 mode. > > Apparently this is an issue for a lot of DSI bridges. But enabling LP-11 for > a bridge is impossible with current documentation [1], which states "A DSI > host should keep the PHY powered down until the pre_enable operation is > called." > Additionally tc358767/tc9595 (DSI-DP bridge) needs LP-11 for AUX channel > access to even get EDID. This is a requirement before pre_enable would > even be possible. > > So some changes to the current flow are needed. But I am not so sure > about LP-11 notification. IMHO a device request to the DSI host to > enable LP-11 seems more sensible. Granted that there can be several DSI devices sharing the DSI bus (aka split-link), I was toying with the idea of making the DSI host call attached DSI devices when the transition happens. I don't have a fully working PoC and I probably won't have it ready til the end of May because of the lack of time and different local priorities. > > Best regards, > Alexander > > [1] https://www.kernel.org/doc/html/latest/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation > > > After everything is > > configured the video stream can finally be enabled. > > > > This means: > > (1) The bridge has to be configured completely in .pre_enable() op > > (with the clock turned on and data lanes in LP-11 mode, thus > > .pre_enable_prev_first has to be set). > > (2) The bridge will enable its output in the .enable() op > > (3) There must be some mechanism before (1) where the bridge can > > release its reset while the clock lane is still in LP-11 mode. > > > > Unfortunately, (3) is crucial for a correct operation of the bridge. > > To satisfy this requriment, introduce a new callback .dsi_lp11_notify() > > which will be called by the DSI host driver. > > > > Signed-off-by: Michael Walle <mwalle@xxxxxxxxxx> > > --- > > drivers/gpu/drm/drm_bridge.c | 16 ++++++++++++++++ > > include/drm/drm_bridge.h | 12 ++++++++++++ > > 2 files changed, 28 insertions(+) > > > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > > index 28abe9aa99ca..98cd6558aecb 100644 > > --- a/drivers/gpu/drm/drm_bridge.c > > +++ b/drivers/gpu/drm/drm_bridge.c > > @@ -1339,6 +1339,22 @@ void drm_bridge_hpd_notify(struct drm_bridge *bridge, > > } > > EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify); > > > > +/** > > + * drm_bridge_dsi_lp11_notify - notify clock/data lanes LP-11 mode > > + * @bridge: bridge control structure > > + * > > + * DSI host drivers shall call this function while the clock and data lanes > > + * are still in LP-11 mode. > > + * > > + * This function shall be called in a context that can sleep. > > + */ > > +void drm_bridge_dsi_lp11_notify(struct drm_bridge *bridge) > > +{ > > + if (bridge->funcs->dsi_lp11_notify) > > + bridge->funcs->dsi_lp11_notify(bridge); > > +} > > +EXPORT_SYMBOL_GPL(drm_bridge_dsi_lp11_notify); > > + > > #ifdef CONFIG_OF > > /** > > * of_drm_find_bridge - find the bridge corresponding to the device node in > > diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h > > index 4baca0d9107b..4ef61274e0a8 100644 > > --- a/include/drm/drm_bridge.h > > +++ b/include/drm/drm_bridge.h > > @@ -630,6 +630,17 @@ struct drm_bridge_funcs { > > */ > > void (*hpd_disable)(struct drm_bridge *bridge); > > > > + /** > > + * dsi_lp11_notify: > > + * > > + * Will be called by the DSI host driver while both the DSI clock > > + * lane as well as the DSI data lanes are in LP-11 mode. Some bridges > > + * need this state while releasing the reset, for example. > > + * Not all DSI host drivers will support this. Therefore, the DSI > > + * bridge driver must not rely on this op to be called. > > + */ > > + void (*dsi_lp11_notify)(struct drm_bridge *bridge); > > + > > /** > > * @debugfs_init: > > * > > @@ -898,6 +909,7 @@ void drm_bridge_hpd_enable(struct drm_bridge *bridge, > > void drm_bridge_hpd_disable(struct drm_bridge *bridge); > > void drm_bridge_hpd_notify(struct drm_bridge *bridge, > > enum drm_connector_status status); > > +void drm_bridge_dsi_lp11_notify(struct drm_bridge *bridge); > > > > #ifdef CONFIG_DRM_PANEL_BRIDGE > > bool drm_bridge_is_panel(const struct drm_bridge *bridge); > > > > > > > -- > TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany > Amtsgericht München, HRB 105018 > Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider > http://www.tq-group.com/ > > -- With best wishes Dmitry
